This invention generally relates to a windmill for capturing and converting the power of the wind to rotational mechanical energy especially to generate electricity and, more particularly, to increasing operational efficiency of the windmill.
Despite its variability, the wind has for a long time been a proven power source to drive mills, pumps, electrical generators and other devices and loads. A so-called horizontal axis windmill has an axis of rotation oriented generally parallel with respect to the surface of the Earth, and has a plurality of blades, vanes, buckets and like propellers rotating about a horizontal axis. The horizontal axis windmill is quite efficient as long as the axis of rotation is aligned with the wind direction. Out of practicality, the horizontal axis windmill is typically provided with means for changing the direction of the horizontal axis as the wind direction changes or has so-called sails of such size that a useful component of power can be derived even from winds of less favorable direction. Large, propeller-type, horizontal axis windmills are typically not built in areas where there is considerable wind turbulence, with quick changes in wind direction and force of the wind. Also, in populated areas, the large propeller-type windmills are generally not considered to be environmentally desirable, principally because of fear that the high-speed propellers may pose safety problems, and also because it has been discovered that the high-speed propellers of giant windmills often create eddies in the wind that travel considerable distances, rattling windows in houses and creating objectionable noise.
A second form of windmill, a so-called vertical axis windmill, has propellers arranged for unitary rotation about a central vertical axis oriented generally perpendicularly with respect to the surface of the Earth and, hence, is operated by wind from any direction. This vertical axis windmill is not as efficient as those with a horizontal axis, since half of the propellers captures the wind for a given wind direction, while the other half does not. Yet, the vertical axis windmill is advantageous in that it has a much lower cost of construction than the horizontal axis windmill; it operates at a much lower noise level that is more readily acceptable in populated areas than the horizontal axis windmill; and it can be locally erected on-site, for example, at one's house, thereby avoiding the need and expense for long-range transmission electrical power lines and step-up and step-down transformers typically used with the horizontal axis windmill.
To compensate for the lower efficiency of the vertical axis windmill, as well as to increase the efficiency of the horizontal axis windmill, the art has proposed using twisted propellers, but portions of these propellers do not work full-time. The art has also proposed adjusting the propellers according to wind speed and direction; however, such adjustable propellers typically do not well withstand high wind conditions. The art has still further proposed using external scoops to collect and channel more wind to the propellers; yet, this construction typically configures the propellers smaller than they would otherwise be. Accordingly, it would be advantageous to further increase the operational efficiency of both the vertical and the horizontal axis windmill without relying solely on these proposed constructions.